1. Field of the Invention
The present invention relates to a bearing device assembly, and, in particular, to an improved bearing device assembly wherein the fixing force of a rotary member mounting seat which is press fitted onto a shaft member of the bearing device assembly is enhanced.
2. Description of the Relevant Art
Prior art bearing device assemblies are those in which a rotary member mounting seat is press fitted onto one axial end of a shaft member having a rolling bearing assembled thereto. an example of this type of bearing device assembly is a cooling water pump shaft of a water-cooled engine.
FIG. 1 shows an assembled water pump shaft comprising a rolling bearing 10 having an outer ring 11, mounted on an intermediate portion of a water pump shaft 12. The bearing 10 is fitted in a housing 31 of a water pump 30. The bearing may be of the ball or roller type. The water pump shaft 12 rotates and serves and the inner bearing ring.
A vane 32 is secured to one axial end 13 of the water pump shaft 12, and a pulley seat 20, for mounting a rotary member, is press fitted to the other axial end 14 of the water pump shaft 12. A driving pulley 40, which is the rotary member, and a cooling fan 42 are secured by bolts 43 to the pulley seat 20. By driving the driving pulley 40 through a belt 44, the vane 32 and the cooling fan 42 are rotated as a unit, using the water pump shaft 12 as a common shaft.
The pulley seat 20 is press fitted to the one axial end 14 of the water pump shaft 12 with an interference clearance of minus 30-70 micrometers. However, in order to fit the pulley seat 20 in proper alignment with the center of the water pump shaft 12, it is necessary to insure a high fitting accuracy. Therefore, the surface of the one axial end 14 of the water pump shaft 12 is highly finished with the chamfering or bevelling angle and the shape of the end face of the end 14 configured so that the smooth fitting can be achieved. Also, it is necessary to prevent drag from being caused on the fitting surface.
The fixing force of the pulley seat 20, which is press fitted to the water pump shaft 12, is affected by such conditions as the viscosity and the amount of rust resisting oil remaining on the fitting surface of the water pump shaft 12 or pulley seat 20, the roughness of the fitting surface, the chamfered shape of the end face of the water pump shaft at which the pulley seat is press fitted, and the speed at which press fitting occurs. For this reason, if these conditions are not appropriate, the fixing force of the pulley seat will be reduced to a great extent.
When the pulley seat fixing force between the pulley seat 20 and the pump shaft 12 is reduced, the pulley seat will move in the axial direction, or slip off of the water pump shaft causing damage to the cooling fan, or a radiator attached to the front side of the cooling fan.
The inventors of the present application found that the main cause of the reduced fixing force between the pulley seat 20 and the pump shaft 12, which results in displacement of the pulley seat 20 along the water pump shaft 12 or the slipping off of the pulley seat 20, is due to the formation of an oil film 52, as shown in FIG. 2, on the fitting surfaces of the pulley seat 20 and water pump shaft 12. Consequently, a boundary friction condition is caused wherein the frictional coefficient of the fitting surface is decreased. In this case, the aforementioned oil film 52 is formed when a rust resisting oil 50 which has been coated on the outer surface of the end portion 14 of the water pump shaft 12 remains on the fitting surface at the time of force fitting the pulley seat 20.